In conventional harvester threshers a straw shaker (vibrating rack) is installed downstream of a threshing device. The mixture of straw and grain arriving from the threshing device is guided by a straw-feed drum onto the shaker. While the straw is transported to the rear, the grain gravitates through the sieve racks of the shaker down onto the sifter. The known shakers have the disadvantage, that the separation effect sharply decreases with larger amounts of straw. This leads to a relatively high loss of grain. The mentioned disadvantages also appear if the load of the shaker is unevenly distributed while working on a slope.
It is known, through U.S. Pat. Ser. No. 513,089, to install a rotating muliple-disk roller close to the straw outlet of the threshing drum, in order to achieve an improvement of the grain separation. The disk roller rotates in the same sense as the threshing drum. The underside of the roller is installed at approximately the same level as the straw outlet of the threshing drum. While the flow of straw emerging from the threshing drum is deflected by the roller downwards onto the straw shaker, the momentum of the grain enables it to maintain its direction and pass through disks of the roller. The grain separated from the straw by this method was collected and conveyed by a device installed behind the mutliple disk roll.
A disadvantage of this arrangement is that the straw thrown downwards onto the shaker by the roller becomes packed. A further disadvantage is the necessary installation and operation of additional conveying devices to feed the separated grain back onto the sifter. The space conditions too are unfavorably affected by the collecting and conveying installation situated above the shaker. Through these additional conveying and driving units the susceptibility of the machine to trouble is highly increased. The expenditure for the construction as described above is considerable.